Process for the production of high concentration alkaline lyes



March 11, 1952 BASlLEWSKY 2,588,469

PROCESS FOR THE PRODUCTION OF HIGH CONCENTRATION ALKALINE LYES Filed July 17, 1947 er Amalgam 7 8 M05277 Steam Wa ter Patented Mar. 11, l952 PRIOCESS'FOR THE PRODUCTIONOF HIGH" QONCENTRATION ALKALINE Alexis Basilewsky, Watermael-Brussels, Belgium,

assignor to Solvay & (lie, Brussels, Belgium, a

Belgian'company Application July 17", 1947, Serial No. 761,702 In Belgium February 18, 1944 Section 1, Public Law 690, August 8, 1946 Patent expires February 18, 1964 (i Claims. (Cl..23:184l) This invention relates to process and apparatus for the decomposition of alkali amalgams with production ofhydrates of corresponding hydroxides having a high content of alkali metal.

It is known that amalgams resulting from the electrolysis of corresponding salts aredecomposed' by water in presence of suitable catalysts; the operation usually takes place in flat bottomed troughs called cells, which operate like shortcircuited cells. The hydroxide solution and the amalgam circulating in counter-current, the solution of highest concentration forms in contact with the richest amalgam. However owing to the diffusion and the tumultuous evolution of hydrogen, the concentration of the solution tends to become uniform throughout the whole length of the cell. This inconvenience is avoided by dividing' the cell into compartments by suitable partitions or by connecting in series a plurality of shorter troughs; these compartments carry connections for the amalgam and for the lye.

It further is known that cells thus constructed do not permit of obtaining high concentrations in alkali hydroxides, the temperature of normal operation not being sufiiciently high; indeed, the most highly concentrated lye, whose temperature should be brought to a maximum, is in contact with the colder amalgam resulting from the electrolysis. Yet it is known that the higher the temperature, the better this will be for the decompo-- sition of the amalgam.

In order to realise better temperature conditions it has been proposed to modify the path of the lye; thus after water has been introduced into the compartment for practically exhausted amalgam, the solution may be circulated in counter current to the amalgam until a predetermined concentration and temperature rise are attained, whereafter it is brought into contact with the amalgam resulting from the electrolysis. I have, on. the other hand, realise an improved circulation by means of an apparatus in whichthe amal gain flows in the same direction from one end of the cell to the other end, while the. lye circulates alternately between the tail compartments and the head compartments up to the compartment of maximum temperature and concentration.

All these apparatus however have the same drawback: the thermal capacity of mercury being. substantially higher than that of aqueous solutions, and the weight of the circulating mercury being far greater than that of the lye in presence, the mercury as it leaves the cell carries: with it a considerable number of calories which are made useless. The heat given out by the reaction-is in deed sufilcient to make it possibletoobtain caustic 2 l'yes having a concentration in say NaOI-I-of'over 80 Up to now however the difficulty remained of recovering this heat from the mercury and giving it' up to the lye at the proper place.

It is the object of my invention to overcomethis difiiculty and more particularly to make use of the water vapor to transfer to the lye the part of the heat of reaction which is not directly transferred thereto, thereby makingit. possible to recuperate almost all said heat.

According to my invention, the heat absorbed by the mercury is used to vaporise part of the water in presence and the vapor thus produced is caused to condense in the lye of highest concentration, so as to raise the temperature of said 1 e and to promote the decomposition. To that end, within the decomposition apparatus itself. which comprises several compartments, the vaporising of water is caused to take place both by direct heat exchange between the mercury and the water and by the heat evolved by the reaction. This vapor then is used to heat the lye in the hottest compartment where the lye reaches the highest concentration, its temperature thus being raised to a maximum. and it will be in a condition to flow from the cell in the form of monohydrate or at still higher concentrations in alkaline hydroxide. The decomposition of the amalgam thus will take place in at least two stages, the second stage taking place in presence of boiling lye, the resulting water vapor being condensed in the lye concentrated by the first stage of decompositibn.

Advantageously, the decomposition of the impoverished amalgam (second or' last stage) is produced by a solution brought to the boiling point, these temperature conditions being most highly favourable to the reaction of decomposi tion. The conclusions of the alkaline hydroxide solution in the mercury are eliminated by water in a manner known per se but, in accordance with the invention, this operation is eiiected in a compartment with a large exchange surface where heat is abandoned by the mercury and the very diluted solution is brought to the boiling point;

An apparatus for carrying out the process, as shown diagrammatically by way of example in the accompanying drawing, comprises at least three chambers or compartments, two with twodecomposition compartments A and B and one heat'exchange compartmentC,'through which the amalgam circulates in the order'A, B, C and the lye in reverse. direction. The compartments A, B, C: are arranged vertically? one above the." other' and: separated by 3. partitions l and 2 provided with passages with non return flaps 3, 4 and a hydraulic seal 5, 6. Compartment A is fitted with the amalgam inlet pipe 1, the hydrogen outlet 8 and lye outlet 9.

This compartment A and the next B carry aloose charge of catalyst or a stack of decomposition grids on which the amalgam flows. After its partial decomposition in compartment A, the amalgam passes through the hydraulic seal 5 into compartment B where its decomposition is completed. The mercury then passes through the hydraulic seal 6 into compartment C which is fitted with trays where it relinquishes heat and it flows out of the cell through the valve ID. The apparatus is completed by a separating cooler D and a steam supply pipe E.

The water enters the bottom part of compartment C which is arranged for example as a column of trays and it circulates in countercurrent to the exhausted mercury coming from compartment B. There the mercury is completely freed from any lye inclusions it may still contain, it yields its heat to the solution the temperature of which rises gradually up to the boiling point and it leaves the apparatus at a temperature near 100 C., while the mixture of water (or of very dilute solution) and water vapor enters compartment B in which takes place the decomposition of the amalgam coming from A. The sensible heat in said amalgam, the reaction heat and eventually a part of the heat produced in C are sufficient to bring the lye in compartment B to the boiling point. The boiling lye then leaves compartment B and together with the steam produced in B and C and with the hydrogen evolved by the reaction of decomposition, it enters compartment A where it will be brought to its maximum concentration by the partial decomposition of the amalgam resulting from the electrolysis. Whereas the heat carried by the amalgam and the reaction heat are not sufficient to raise the temperature of the lye to the requisite degree, the complmentary heat is supplied by the condensation of the water vapor from the preceding compartments.

It is thus seen that, in accordance with the invention, the transfer of heat from the mercury to the lye does not take place solely by direct contact, as the weights brought into play do not permit of reaching the desired; result, but this transfer is effected mainly through the medium of water vapor which takes its heat of vaporization from the heat of the mercury and gives it back as it condenses in the lye to be heated.

By way of a non limitating example, there is introduced simultaneously 2390 kgs. of sodium amalgam at 0.5% Na, at 70 C. into compartment A and 17.6 kgs. of water at C. into the hydrogen cooler D where said water is brought to 50 C., whereupon it enters compartment C where it comes into contact with the mercury resulting from the decomposition of the amalgam. The Water is brought to the boiling point, about one sixth thereof being vaporised while the mercury flows out of the cell at a temperature of 99 C.

The mixture of water and steam at 104 C. enters compartment B where the decomposition reaction is completed in presence of boiling lye containing 32% NaGH. The quantity of steam is raised to about 8 kgs. superheated to 120 C.

Steam and boiling lye enter compartment A where the decomposition of the amalgam raises the NaOH concentration of the solution to 75%,

the decomposition being favoured by the supply of heat from the preceding compartment, the temperature in A being C.

If, for some fortuitous cause, the solution in B should not be boiling, the vaporisation heat taken from C would be absorbed by said solution until it reaches the boiling point, and thereafter, the operating temperature having been reached, the steam from C will pass through compartment B and, together with the steam produced in said compartment, it will heat the lye of A.

When starting the operation of the cell, as long as the operating temperature is not reached, extraneous heat is supplied by introducing steam at E. This extraneous source of heat may also play an important part in the operation of the cell. Thus for example, if it is desired still further to raise the concentration of the lyes, the introduction of extraneous heat makes it possible to raise to that end the operating tem erature and pressure conditions in the apparatus. This modification of conditions is also advantageous from other points of view: in addition to improving the conditions of description of the amalgam, it permits of improving the pressure conditions of the hydrogen evolved. Without the use of extraneous steam the process and apparatus as described supply hydrogen at a pressure which already is high enough to make its distribution and its use possible without supplementary compression, but with introduction of extraneous heat, the apparatus being able to operate under higher pressure conditions, it is further made possible to dispense with pumping the lyes, the latter being under pressure as they leave the apparatus. The injection of extraneous vapors, although not indispensable to carrying out the process according to the invention, thereof will often be advantageous, not only when starting the operation of the cell, but also during its normal operation. It can be performed so as to supply a more or less important part, or even the whole of the amount of water necessary to the constitution of the lyes in operation. 1

Under operating conditions in the apparatus, relatively large quantities of mercury and water are carried away by the hydrogen; they are recuperated by passing the hydrogen through a separating condensor cooled by the supply water of the cell, the products of condensation and/or separation returning to the cell while the hydrogen leaves the said apparatus.

It is to be understood that the drawing of the apparatus as illustrated is given merely to show its principle, as the device may be realised in many forms and modifications within the scope of the invention. For example the connection for the amalgam between the compartments may be carried outsidethe cell, the compartments may be arranged in stepped relation, they may be subdivided into groups of smaller elements at increasing temperature and concentration, each group as a whole operating like the subdivided original compartment; or in the subdivided cell, the order of the elements may be changed, thus the lye comin out of any compartment may be led to the next after having passed through another compartment of the same group. The enumeration of these modifications is of course not restrictive.

I claim:

1. A process of producing alkali metal hydroxide solutions of high concentration by de composing the corresponding amalg'ams which comprises establishing a plurality of vertically superimposed confined reaction zones containing alkali metal hydroxide solution, the solution in each of said zones increasing in alkali metal concentration from a lowermost zone of least concentration to an uppermost zone of highest con-- centration, causing the amalgam to flow unidirectionally in the direction of the zone of least alkali metal hydroxide concentration, thereby becoming gradually exhausted of alkali metal, in troducing water into the zone of least alkali metal hydroxide concentration, withdrawing the exhausted amalgam in contact with said water to efiect vaporization of at least some of said water by the sensible heat in said exhausted amalgam, introducing the water vapor thus produced and the alkali metal solution of least concentration into an alkali metal hydroxide solution of higher concentration to condense said vapor, thereby raising the temperature of said alkali metal hydroxide solution, introducing the vapors and liquid contained in each of said zones of alkali metal hydroxide solution into the body of the solution of next higher alkali metal hydroxide concentration, and withdrawing solution from the zone of highest alkali metal hydroxide concentration.

2. A process for the production of alkali metal hydroxide solutions of high concentration by decomposing the corresponding amalgam which comprises establishing a plurality of adjoining bodie of alkali metal hydroxide solutions of increasing concentration including a lowermost body of least concentration and an uppermost body of highest concentration, said bodies being disposed in interconnected vertically superim posed relationship, causing 'the amalgam to flow unidirectionally in contact with said bodies in the direction of the body of least alkali metal hy droxide solution, causing the alkali metal hydroxide solution to flow counter-currently to tne flow of said amalgam, the flow of alkali metal hydroxide solution passing from the top of one body into the lower portion of the next superimposed succeeding body, and simultaneously causing the vapors generated by each body of alkali metal hydroxide solution to flow into the lower portion of the next succeeding body of higher alkali metal hydroxide solution and to bubble upwardly therethrough and condense 'therein, thereby raising the temperature of said alkali metal hydroxide solution and promoting decomposition of said amalgam.

3. In a process for the production of alkali metal hydroxide solutions of high concentration by decomposing the corresponding amalgam, the steps which comprise flowing water upwardly through a plurality of interconnected vertically superimposed zones, flowing an alkali metal amalgam counter-currently in contact with the Water in said zones, whereby to decompose said alkali metal amalgam and to produce alkali metal hydroxide solutions of gradually increasing concentration including an uppermost zone of highest concentration and a lowermost zone of least concentration and to substantially completely exhaust the alkali metal from said amalgam, introducing water into the zone of least alkali metal hydroxide solution, withdrawing the exhausted amalgam in contact with said water to effect vaporization of at least some of said water by the sensible heat in said exhausted amalgam, and introducing the solution from said zone of least concentration and the water vapor thus produced 4. In a process as defined in claim 3, the step which comprises introducing at least a part 01 said water in the form of water vapor into said last zone of least concentration.

5. A process as defined in claim 3, wherein the said zones are maintained under super-atmospheric pressure.

6. In a process for the production of alkali metal hydroxide solutions of high concentration, the steps which comprise flowing water unidirectionally upwardly through a plurality of interconnected vertically superimposed zones, flowing an alkali metal amalgam counter-currently in contact with said water in said zones, whereby to produce alkali metal hydroxide solutions disposed in an uppermost first zone of highest concentration, a lowermost last zone of least concentration and at least one intermediate zone of alkali metal hydroxide solution of intermediate concentration, said amalgam flowing in the direction of said last zone of least concentration, thereby becoming gradually exhausted of alkali metal, introducing water into the said last zone of least alkali metal hydroxide concentration, withdrawing the exhausted amalgam in contact with said water to effect vaporization of at least some of said water by the sensible heat in said exhausted amalgam, introducing the water vapor thus produced and the alkali metal hydroxide solution in said lowermost zone of least concentration into an alkali metal hydroxide solution in said intermediate zone, the solution in said intermediate zone being caused to boil in the presence of the amalgam and the vapor from said preceding zone, causing the vapor produced in said intermediate zone and the alkali metal hydroxide solution therein to pass into the alkali metal hydroxide solution contained in said first zone of highest concentration, and withdrawing concentrated alkali metal hydroxide solution from said first zone.

ALEXIS BASILEWSKY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 679,355 Barr July 30, 1901 728,746 McCaffrey May 19, 1903 1,532,489 Heinze Apr. 7, 1925 1,704,909 Bencker Mar. 12, 1929 1,753,015 McGregor Apr. 1, 1930 1,784,066 Heinze Dec. 9, 1930 1,945,114 Lachman Jan. 30, 1934 2,009,347 Sheldon July 23, 1935 2,091,709 Hampton Aug. 31, 1937 2,154,144 Albin Apr. 11, 1939 2,191,919 Thayer Feb. 27, 1940 2,405,158 Mensing Aug. 6, 1946 FOREIGN PATENTS Number Country Date 4,448 Great Britain 1874 10,352 Great Britain 1909 415,466 Great Britain Aug. 27, 1934 452,302 Great Britain Aug. 30, 1936 453,517 Great Britain 1936 

1. A PROCESS OF PRODUCING ALKALI METAL HYDROXIDE SOLUTIONS OF HIGH CONCENTRATION BY DECOMPOSING THE CORRESPONDING AMALGAMS WHICH COMPRISES ESTABLISHING A PLURALITY OF VERTICALLY SUPERIMPOSED CONFINED REACTION ZONES CONTAINING ALKALI METAL HYDROXIDE SOLUTION, THE SOLUTION IN EACH OF SAID ZONES INCREASING INALKALI METAL CONCENTRATION FROM A LOWERMOST ZONE OF LEAST CONCENTRATION TO AN UPPERMOST ZONE OF HIGHEST CONCENTRATION, CAUSING THE AMALGAM TO FLOW UNIDIRECTIONALLY IN THE DIRECTION OF THE ZONE OF LEAST ALKALI METAL HYDROXIDE CONCENTRATION, THERERBY BECOMING GRADUALLY EXHAUSTED OF ALALI METAL, INTRODUCING WATER INTO THE ZONE OF LEAST ALKALI METAL HYDROXIDE CONCENTRATION, WITHDRAWING THE EXHAUSTED AMALGAM IN CONTACT WITH SAID WATER TO EFFECT VAPORIZATION OF AT LEAST SOME OF SAID WATER BY THE SENSIBLE HEAT IN SAID EXHAUSTED AMALGAM, INTRODUCING THE WATER VAPOR THUS PRODUCED AND THE ALKALI METAL SOLUTION OF LEAST CONCENTRATION INTO AN ALKALI METAL HYDOXIDE SOLUTION OF HIGHER CONCENTRATION TO CONDENSE SAID VAPOR, THEREBY RAISING THE TEMPERATURE OF SAID ALKALI METAL HYDROXIDE SOLUTION, INTRODUCING THE VAPORS AND LIQUID CONTAINED IN EACH OF SAID ZONES OF ALKALI METAL HYDROXIDE SOLUTION INTO THE BODY OF THE SOLUTION OF NEXT HIGHER ALKALI METAL HYDROXIDE CONCENTRATION, AND WITHDRAWING SOLUTION FROM THE ZONE OF HIGHEST ALKALI METAL HYDROXIDE CONCENTRATION. 